The present invention relates to methods and apparatuses for use in treating proliferative tissue disorders, and more particularly to methods and apparatus for controlling the positioning of a radiation therapy apparatus with respect to the sensitive tissue.
Malignant tumors are often treated by surgical resection of the tumor to remove as much of the tumor as possible. Infiltration of the tumor cells into normal tissue surrounding the tumor, however, can limit the therapeutic value of surgical resection because the infiltration can be difficult or impossible to treat surgically. Radiation therapy can be used to supplement surgical resection by targeting the residual tumor margin after resection, with the goal of reducing its size or stabilizing it. Radiation therapy can be administered through one of several methods, or a combination of methods, including external-beam radiation, stereotactic radiosurgery, and permanent or temporary interstitial brachytherapy. The term xe2x80x9cbrachytherapy,xe2x80x9d as used herein, refers to radiation therapy delivered by a spatially confined radioactive material inserted into the body at or near a tumor or other proliferative tissue disease site. Owing to the proximity of the radiation source, brachytherapy offers the advantage of delivering a more localized dose to the target tissue region.
Brachytherapy can be performed by implanting radiation sources directly into the tissue to be treated. Interstitial brachytherapy is traditionally carried out using radioactive seeds such as 125I seeds. These seeds, however, produce inhomogeneous dose distributions. In order to achieve a minimum prescribed dosage throughout a target region of tissue, high activity seeds must be used, resulting in very high doses being delivered in some regions in proximity to the seed or seeds which can cause radionecrosis in healthy tissue. Interstitial brachytherapy is useful for treating malignant brain and breast tumors, among others.
The absorbed dose rate in a target tissue exterior to a radioactive source is inversely proportional to the square of the distance between the radiation source and the target point. As a result, where the radioactive source has sufficient activity to deliver a prescribed dose, say 2 centimeters into the target tissue, the tissue directly adjacent the wall of the distensible reservoir, where the distance to the radioactive source is very small, may still be overly xe2x80x9chotxe2x80x9d to the point where sensitive but otherwise healthy tissue necrosis may result.
In general, the amount of radiation desired by the physician is a certain minimum amount that is delivered to a region up to about two centimeters away from the wall of the excised tumor. It is desirable to keep the radiation that is delivered to the tissue in the target treatment region within a narrow absorbed dose range to prevent over-exposure to tissue at or near the radiation source, while still delivering the minimum prescribed dose at the maximum prescribed distance from the radiation source. It is also desirable, at least in some applications, to provide these advantages while tailoring the radiation dosage to avoid fully dosing sensitive tissue or to reduce the amount of radiation that escapes the patient""s body.
Thus, there is a need for an instrument which can be used to deliver radiation from a radioactive source to target tissue within the human body with a desired intensity and at a predetermined distance from the radiation source without over-exposure of sensitive body tissues, such as skin or organ tissue for example, disposed proximate to the radiation.
The present invention provides a positioning or spacing apparatus and methods of use for positioning a radiotherapy device, such as a brachytherapy device, at a distance apart from the outer surface of the tissue proximate to a surgical extraction site. The spacing apparatus is useful in that the instrument is effective to limit the amount of radiation that comes into contact with the adjacent tissue, and thereby protect sensitive tissue from overheating or hotspots, and/or protect against radiation exposure outside of the patient""s body which may affect healthcare providers or others who might come close to the patient.
In general, the spacing apparatus according to the present invention includes a spacing element that can have any shape and size, but is preferably adapted to provide a sufficient amount of space, hereinafter referred to as the desired spacing, between the brachytherapy device and the outer surface of the tissue adjacent the extraction site. The desired spacing is preferably adapted to prevent damage to healthy tissue cells, while allowing cancerous cells to be destroyed. The spacing apparatus can be mated to or disposed in conjunction with a brachytherapy device, or alternatively, can be introduced via a separate insertion device for use with any brachytherapy device. The size and shape of the spacing element can vary, and the spacing element can be movable between an open position and a closed position.
In one embodiment, the spacing element is formed from an expandable balloon member. In the closed, deflated position, the balloon member is disposed or folded around an insertion member to allow the insertion member to be inserted through an opening, e.g. an introducer sheath, into a surgical extraction site. Once inserted, the balloon member can be inflated to the open position to provide a predetermine amount of space between a brachytherapy device and the tissue surrounding the extraction site. The necessary spacing is preferably equal to the height of the spacing element which is predeterminablexe2x80x94that is, the height can be fixed and predetermined, or the spacing element can be of a variable height that is selectable in use. The balloon member can have a preformed shape such that, when inflated, the balloon member is effective to provide the necessary spacing between the brachytherapy device and the adjacent tissue.
In another embodiment, the spacing element is formed from a shape memory material and is biased to the open position, in which the spacing element has a three-dimensional shape. The three-dimensional shape can be, for example, a disk-shaped member which folds around the insertion member. In another embodiment, the spacing element can have a substantially folded V-shape in the closed position, and can be substantially L-shaped in the open position. In use, the spacing element is biased into the closed position by an introducer sheath during insertion into the surgical extraction site and, once fully inserted, is free to move to the open position to provide the necessary amount of spacing between the brachytherapy device and the sensitive tissue proximate to the extraction site.
In other aspects of the invention, a brachytherapy device is provided having an insertion member with proximal and distal ends, a first expandable balloon member disposed on the distal end of the insertion member, and a spacing element disposed on the distal end of the insertion member proximal to the first expandable balloon member. The expandable balloon member is effective to receive a radiation source for treating target tissue surrounding a surgical extraction site, and the spacing element is effective to position the expandable balloon member at a distance apart from the tissue surrounding the extraction site. The spacing element of the brachytherapy device can be movable between an open position and a closed position, and can be formed from an expandable balloon member, a shape memory material, or other similar structures. In a preferred embodiment, the first expandable balloon member, upon inflation, is effective to move the spacing element from a closed position to an open position.
In another embodiment of the present invention, a brachytherapy system is provided having a brachytherapy device for treating target tissue surrounding a surgical extraction site, and a spacing apparatus for positioning the brachytherapy device at a distance apart from sensitive tissue proximate to the surgical extraction site. The spacing apparatus can include an insertion member having proximal and distal ends, and a spacing element disposed on the distal end of the insertion member.
The present invention also provides methods for positioning a brachytherapy device at a distance apart from tissue surrounding a surgical extraction site. In one embodiment, the method can include the steps of introducing a spacing apparatus having a predeterminable height into a surgical extraction site, introducing a brachytherapy device for treating target tissue into the surgical extraction site, and positioning the spacing apparatus with respect to the brachytherapy device so as to position the device at a distance equal to the height of the spacing element apart from the tissue surrounding the surgical extraction site. The spacing apparatus and the brachytherapy device can be introduced into the surgical extraction site through separate entrances ports, or though the same entrance port. Moreover, the spacing apparatus can be mated to or formed integrally with the brachytherapy device.